Ablation of myocardial tissue is well known as a treatment for cardiac arrhythmias. In radio-frequency (RF) ablation, for example, a catheter is inserted into the heart and brought into contact with tissue at a target location. RF energy is then applied through an electrode on the catheter in order to create a lesion for the purpose of breaking arrhythmogenic current paths in the tissue.
Recently, circumferential ablation of the ostia of the pulmonary veins has gained acceptance as a treatment for atrial arrhythmias, and particularly for atrial fibrillation. For example, U.S. Patent Application Publication 2005/0033135, whose disclosure is incorporated herein by reference, describes a lasso for pulmonary vein mapping and ablation. A catheter for circumferentially mapping a pulmonary vein (PV) includes a curved section shaped to generally conform to the shape of the interior surface of the PV. The curved section comprises one or more sensing electrodes, and its proximal end is joined at a fixed or generally known angle to a base section of the catheter. The catheter is inserted into the heart, and the curved section is positioned in contact with the wall of the PV, while the base section remains within the left atrium, typically positioned such that the joint with the curved section is at the ostium of the vein. The sensing electrodes may additionally perform ablation of selected sites, or the catheter may further comprise ablation elements.
U.S. Patent Application Publication 2010/0168548, whose disclosure is incorporated herein by reference, describes a lasso catheter for use in a system for electrical mapping of the heart. The catheter has an array of raised, perforated electrodes, which are in fluid communication with an irrigating lumen. There are position sensors on a distal loop section and on a proximal base section of the catheter. The electrodes are sensing electrodes that may be adapted for pacing or ablation. The raised electrodes securely contact cardiac tissue, forming electrical connections having little resistance.
U.S. Patent Application Publication 2008/0281312 describes an ablation therapy system and systematic method for treating continuous atrial fibrillation. A carrier assembly and flexible outer catheter tube are percutaneously advanced over a guide wire whose distal end has been inserted into a pulmonary vein of the patient. After proper deployment of the carrier assembly, and after proper orientation and location of the electrodes relative to the targeted PV tissue, the carrier assembly is advanced distally, as a unit, along the guide wire to contact with the ostial tissue surrounding the Left Superior Pulmonary Vein (LSPV). Once sufficient tissue contact has been established, and the mapping procedure has confirmed the presence of aberrant conductive pathways, ablation energy may be passed through the output electrodes.